[ITK-users] AffineTransform to 4x4 matrix...again maybe

[vincent ngai]

Hi Bradley,

Hmm, GetCenter() negated should be the same as InvCRM. I'll flip the order
of the multiplication and see what happens, it could be the C++ operator*()
order being different from the way its written. Its so annoying to get the
results close but not exact :(

Thanks


On Tue, Aug 5, 2014 at 9:12 PM, Bradley Lowekamp <blowekamp at mail.nih.gov>
wrote:

> Hello,
>
> That looks pretty close, but I think CRM[12,13,14] should be -GetCenter(),
> with the negative there.  Then the TM should be applied last, using your
> original notation with the previously mentioned correction I'd expect this
> to be correct:
>
> OGLM = TM * InvCRM * Rot * CRM
>
> Hope that helps,
> Brad
>
> [1]
> http://www.itk.org/Doxygen/html/classitk_1_1MatrixOffsetTransformBase.html
>
> On Aug 5, 2014, at 5:26 AM, vincent ngai <vincent.ngai at gmail.com> wrote:
>
> > Hi all, apologies if this has been asked before, I googled the above but
> only got 4x4 -> AffineTransform and not the other way around.
> >
> > I need to get the output of an AffineTransform after registration to my
> OpenGL renderer.
> >
> > From what I understand, the AffineTransform is composed of a Rotation,
> Center of Rotation and Translation.
> >
> > So would the following sequence of 4x4 transformation be correct?
> >
> > OGLM = InvCRM * Rot * CRM * TM
> >
> > where
> >
> > CRM      = 4x4 identity matrix with indices [ 12, 13, 14] set to XYZ
> value of GetCenter()
> > InvCRM  = Inverse of CRM
> > Rot        = 4x4 Identity matrix with 3x3 set to the rotation parameters
> > TM        = 4x4 identity matrix with indicies[ 12, 13, 14 ] set to the
> translation parameters
> >
> > Essentially:
> >
> > 1) translate center to origin
> > 2) perform rotation
> > 3) translate back to where we were
> > 4) slap on translation
> >
> > I am doing the above, but for some reason the translation does not match
> up. The rotation seems fine.
> > --
> > Regards,
> > Vincent
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-- 
Regards,
Vincent
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